The present invention relates to a continuously variable transmission, and more particularly to a shift control apparatus thereof.
Generally, a continuously variable transmission (CVT) has been arranged to continuously change the gear ratio. Accordingly, it is possible to execute the shift control of the CVT so as to transfer an engine power to wheels while maintaining the engine rotation speed at a value in which an engine outputs the maximum engine output torque. Further, such a CVT effectively operates to improve the energy consumption or vehicle dynamic performance by properly selecting a gear ratio according to a driving condition of a vehicle. Normally, such a CVT is arranged to execute the shift control in the following manner. First, a target value of the transmission input rotation speed is obtained from the measured engine throttle opening degree and the vehicle speed on the basis of a previously defined shift map relating the combination of the engine throttle opening degree (engine load) and the vehicle speed (transmission output rotation speed). Then, The gear ratio is continuously changed such that the transmission input rotation speed corresponds to the target value.
Japanese Patent Provisional Publication No. 8-145139 discloses a conventional shift control apparatus of a CVT. The conventional shift control apparatus is arranged to suppress the change of the gear ratio according to the increase of a shift speed, which is a speed for executing shifting. On the other hand, another conventional shift control apparatus is arranged to increase such a shift speed for shifting when the vehicle is quickly accelerated or quickly braked.
However, these conventional shift control apparatuses are arranged to change the shift speed pattern on the basis of the previously defined shift map or to change the shift map with respect to the predetermined shift speed pattern. That is, the conventional shift control apparatuses are arranged to change only one of the shift map and the shift speed pattern. Therefore, it is difficult to execute the shift control according to the vehicle driving condition such as the vehicle speed, the lateral and longitudinal accelerations, the slope degree of a road. Further, since the demand as to the shift response is largely different among individuals (drivers), it is impossible to design the CVT performing a shift speed satisfied by all drivers. It is desirable for the shift response of the CVT to be changed according to the driver's liking. However, the conventional shift control apparatuses have not been arranged to satisfy such driver's liking.